Thorsten Weber | Lawrence Berkeley National Laboratory (original) (raw)
Papers by Thorsten Weber
Physical Review Letters, 2018
We report on a direct method to measure the interatomic potential energy curve of diatomic system... more We report on a direct method to measure the interatomic potential energy curve of diatomic systems. A COLTRIMS reaction microscope was used to measure the squares of the vibrational wave functions of H 2 , He 2 , Ne 2 , and Ar 2. The Schrödinger equation relates the curvature of the wave function to the potential V(R) and therefore offers a simple but elegant way to extract the shape of the potential.
Physical Review Letters, 2016
We investigate the photo-doubleionization of H2 molecules with 400 eV photons. We find that the e... more We investigate the photo-doubleionization of H2 molecules with 400 eV photons. We find that the emitted electrons do not show any sign of two-center interference fringes in their angular emission distributions if considered separately. In contrast, the quasi-particle consisting of both electrons (i.e. the "dielectron") does. The work highlights the fact that non-local effects are embedded everywhere in nature where many-particle processes are involved. Introduction: The two most counterintuitive cornerstones of quantum mechanics are the superposition principle giving rise to interference phenomena, and entanglement between distinct particles establishing what Einstein called "spooky action at a distance". A phenomenon which can only be explained by combining both these effects is two-particle interference [1], where the
The Journal of Chemical Physics
We present an experimental and theoretical energy- and angle-resolved investigation on the non-di... more We present an experimental and theoretical energy- and angle-resolved investigation on the non-dissociative photoionization dynamics of near-resonant, one-color, two-photon, single valence ionization of neutral O2 molecules. Using 9.3 eV femtosecond pulses produced via high harmonic generation and a 3-D momentum imaging spectrometer, we detect the photoelectrons and [Formula: see text] cations produced from one-color, two-photon ionization in coincidence. The measured and calculated photoelectron angular distributions show agreement, which indicates that a superposition of two intermediate electronic states is dominantly involved and that wavepacket motion on those near-resonantly populated intermediate states does not play a significant role in the measured two-photon ionization dynamics. Here, we find greater utility in the diabatic representation compared to the adiabatic representation, where invoking a single valence-character diabat is sufficient to describe the underlying two...
We present an experimental study on the photoionization dynamics of non-resonant 2-photon single ... more We present an experimental study on the photoionization dynamics of non-resonant 2-photon single valence ionization of neutral argon atoms. Using 9.3 eV photons produced via high harmonic generation and a 3-D momentum imaging spectrometer, we detect the photoelectrons and ions produced from 2-photon above-threshold ionization in coincidence. Photoionization from the 3p orbital produces a photoelectron scattering wave function with p and f partial wave components, which interfere and result in a photoelectron angular distribution with peak amplitude perpendicular to the VUV polarization. The comparison between the present results and two previous sets of theoretical calculations [Pan, C. Starace, A. F. (1991). Physical Review A, 44(1), 324., and Moccia, R., Rahman, N. K., Rizzo, A. (1983). Journal of Physics B: Atomic and Molecular Physics, 16(15), 2737.] indicates that electron-electron correlation contributes appreciably to the 2-photon ionization dynamics.
Bulletin of the American Physical Society, 2016
x-ray photoelectron spectroscopy techniques for real-time studies of
Nature Communications
The double photoionization of a molecule by one photon ejects two electrons and typically creates... more The double photoionization of a molecule by one photon ejects two electrons and typically creates an unstable dication. Observing the subsequent fragmentation products in coincidence can reveal a surprisingly detailed picture of the dynamics. Determining the time evolution and quantum mechanical states involved leads to deeper understanding of molecular dynamics. Here in a combined experimental and theoretical study, we unambiguously separate the sequential breakup via D+ + OD+ intermediates, from other processes leading to the same D+ + D+ + O final products of double ionization of water by a single photon. Moreover, we experimentally identify, separate, and follow step by step, two pathways involving the b 1Σ+ and a 1Δ electronic states of the intermediate OD+ ion. Our classical trajectory calculations on the relevant potential energy surfaces reproduce well the measured data and, combined with the experiment, enable the determination of the internal energy and angular momentum di...
Physical Review Letters, 2007
Using H 2 and D 2 , we observe two-surface population dynamics by measuring the kinetic energy of... more Using H 2 and D 2 , we observe two-surface population dynamics by measuring the kinetic energy of the correlated ions that are created when H 2 (D 2) ionize in short (40-140 fs) and intense (10 14 W=cm 2) infrared laser pulses. Experimentally, we find a modulation of the kinetic energy spectrum of the correlated fragments. The spectral progression arises from a hitherto unexpected spatial modulation on the excited state population, revealed by Coulomb explosion. By solving the two-level time-dependent Schrödinger equation, we show that an interference between the net-two-photon and the one-photon transition creates localized electrons which subsequently ionize.
We present state-selective measurements on the NH_2^+ + H^+ and NH^+ + H^+ + H dissociation chann... more We present state-selective measurements on the NH_2^+ + H^+ and NH^+ + H^+ + H dissociation channels following single-photon double ionization at 61.5 eV of neutral NH_3, where the two photoelectrons and two cations are measured in coincidence using 3-D momentum imaging. Three dication electronic states are identified to contribute to the NH_2^+ + H^+ dissociation channel, where the excitation in one of the three states undergoes intersystem crossing prior to dissociation, producing a cold NH_2^+ fragment. In contrast, the other two states directly dissociate, producing a ro-vibrationally excited NH_2^+ fragment with roughly 1 eV of internal energy. The NH^+ + H^+ + H channel is fed by direct dissociation from three intermediate dication states, one of which is shared with the NH_2^+ + H^+ channel. We find evidence of autoionization contributing to each of the double ionization channels. The distributions of the relative emission angle between the two photoelectrons, as well as the ...
We investigate ultrafast dynamics of the lowest singlet excited electronic state in liquid nitrob... more We investigate ultrafast dynamics of the lowest singlet excited electronic state in liquid nitrobenzene using Ultrafast Transient Polarization Spectroscopy (UTPS), extending the well-known technique of Optical-Kerr Effect (OKE) spectroscopy to excited electronic states. The third-order non-linear response of the excited molecular ensemble is highly sensitive to details of excited state character and geometries and is measured using two femtosecond pulses following a third femtosecond pulse that populates the S1 excited state. By measuring this response as a function of time delays between the three pulses involved, we extract the dephasing time of the wave-packet on the excited state. The dephasing time measured as a function of time-delay after pump excitation shows oscillations indicating oscillatory wave-packet dynamics on the excited state. From the experimental measurements and supporting theoretical calculations, we deduce that the wave-packet completely leaves the S1 state su...
We present state-selective measurements on the NH_2^+ + H^+ and NH^+ + H^+ + H dissociation chann... more We present state-selective measurements on the NH_2^+ + H^+ and NH^+ + H^+ + H dissociation channels following single-photon double ionization at 61.5 eV of neutral NH_3, where the two photoelectrons and two cations are measured in coincidence using 3-D momentum imaging. Three dication electronic states are identified to contribute to the NH_2^+ + H^+ dissociation channel, where the excitation in one of the three states undergoes intersystem crossing prior to dissociation, producing a cold NH_2^+ fragment. In contrast, the other two states directly dissociate, producing a ro-vibrationally excited NH_2^+ fragment with roughly 1 eV of internal energy. The NH^+ + H^+ + H channel is fed by direct dissociation from three intermediate dication states, one of which is shared with the NH_2^+ + H^+ channel. We find evidence of autoionization contributing to each of the double ionization channels. The distributions of the relative emission angle between the two photoelectrons, as well as the ...
Review of Scientific Instruments
We report a novel experimental technique to investigate ultrafast dynamics in photoexcited molecu... more We report a novel experimental technique to investigate ultrafast dynamics in photoexcited molecules by probing the 3 rd-order nonlinear optical susceptibility. A non-colinear 3-pulse scheme is developed to probe the ultrafast dynamics of excited electronic states using the optical Kerr effect. Optical homodyne and optical heterodyne detection are demonstrated to measure the 3 rdorder nonlinear optical response for the S 1 excited state of liquid nitrobenzene, which is populated by 2-photon absorption of a 780 nm 40 fs excitation pulse.
Physical Chemistry Chemical Physics
3D momentum imaging investigation of the dynamics of dissociative electron attachment to formic a... more 3D momentum imaging investigation of the dynamics of dissociative electron attachment to formic acid, producing a hydride anion and either formyloxyl or hydrocarboxyl radicals.
Nature communications, Jan 22, 2017
The toolbox for imaging molecules is well-equipped today. Some techniques visualize the geometric... more The toolbox for imaging molecules is well-equipped today. Some techniques visualize the geometrical structure, others the electron density or electron orbitals. Molecules are many-body systems for which the correlation between the constituents is decisive and the spatial and the momentum distribution of one electron depends on those of the other electrons and the nuclei. Such correlations have escaped direct observation by imaging techniques so far. Here, we implement an imaging scheme which visualizes correlations between electrons by coincident detection of the reaction fragments after high energy photofragmentation. With this technique, we examine the H2 two-electron wave function in which electron-electron correlation beyond the mean-field level is prominent. We visualize the dependence of the wave function on the internuclear distance. High energy photoelectrons are shown to be a powerful tool for molecular imaging. Our study paves the way for future time resolved correlation i...
Molecular Physics, 2012
This article may be used for research, teaching, and private study purposes. Any substantial or s... more This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
Physical chemistry chemical physics : PCCP, Jan 15, 2018
We present a combined experimental and theoretical investigation of the electron dynamics and bod... more We present a combined experimental and theoretical investigation of the electron dynamics and body-frame angular dependence of valence photo-single ionization of CF4 and subsequent dissociation into CF3+ and F. Ionization from a valence t2 orbital shows overlapping shape resonances close to threshold that couple to the same total symmetry, leading to striking changes in the photoelectron angular distributions when viewed in the body-frame.
Abstract—We have developed a delay-line readout technique for microchannel plate detectors with a... more Abstract—We have developed a delay-line readout technique for microchannel plate detectors with an increased acceptance for multiple hit events compared to standard two-layer delay-line an-odes. This technique allows unambiguous determination of arrival time and position of at least two simultaneously detected particles, and/or to detect an even larger number of particles in a shower, as long as any two particles do not arrive both at the same time and at the same position within certain limits. We demonstrate and dis-cuss the abilities and limitations of this technique and the relevance for certain experimental tasks. Index Terms—Delay line, fragment imaging, imaging, micro-channel plate, multihit, three-dimensional (3-D) detection. I.
Chemical Science
We investigate interatomic Coulombic decay in NeKr dimers after neon inner-valence photoionizatio... more We investigate interatomic Coulombic decay in NeKr dimers after neon inner-valence photoionization [Ne+(2s-1)] using a synchrotron light source. We measure with energy resolution the two singly charged ions of the...
Physical Review Letters, 2018
We report on a direct method to measure the interatomic potential energy curve of diatomic system... more We report on a direct method to measure the interatomic potential energy curve of diatomic systems. A COLTRIMS reaction microscope was used to measure the squares of the vibrational wave functions of H 2 , He 2 , Ne 2 , and Ar 2. The Schrödinger equation relates the curvature of the wave function to the potential V(R) and therefore offers a simple but elegant way to extract the shape of the potential.
Physical Review Letters, 2016
We investigate the photo-doubleionization of H2 molecules with 400 eV photons. We find that the e... more We investigate the photo-doubleionization of H2 molecules with 400 eV photons. We find that the emitted electrons do not show any sign of two-center interference fringes in their angular emission distributions if considered separately. In contrast, the quasi-particle consisting of both electrons (i.e. the "dielectron") does. The work highlights the fact that non-local effects are embedded everywhere in nature where many-particle processes are involved. Introduction: The two most counterintuitive cornerstones of quantum mechanics are the superposition principle giving rise to interference phenomena, and entanglement between distinct particles establishing what Einstein called "spooky action at a distance". A phenomenon which can only be explained by combining both these effects is two-particle interference [1], where the
The Journal of Chemical Physics
We present an experimental and theoretical energy- and angle-resolved investigation on the non-di... more We present an experimental and theoretical energy- and angle-resolved investigation on the non-dissociative photoionization dynamics of near-resonant, one-color, two-photon, single valence ionization of neutral O2 molecules. Using 9.3 eV femtosecond pulses produced via high harmonic generation and a 3-D momentum imaging spectrometer, we detect the photoelectrons and [Formula: see text] cations produced from one-color, two-photon ionization in coincidence. The measured and calculated photoelectron angular distributions show agreement, which indicates that a superposition of two intermediate electronic states is dominantly involved and that wavepacket motion on those near-resonantly populated intermediate states does not play a significant role in the measured two-photon ionization dynamics. Here, we find greater utility in the diabatic representation compared to the adiabatic representation, where invoking a single valence-character diabat is sufficient to describe the underlying two...
We present an experimental study on the photoionization dynamics of non-resonant 2-photon single ... more We present an experimental study on the photoionization dynamics of non-resonant 2-photon single valence ionization of neutral argon atoms. Using 9.3 eV photons produced via high harmonic generation and a 3-D momentum imaging spectrometer, we detect the photoelectrons and ions produced from 2-photon above-threshold ionization in coincidence. Photoionization from the 3p orbital produces a photoelectron scattering wave function with p and f partial wave components, which interfere and result in a photoelectron angular distribution with peak amplitude perpendicular to the VUV polarization. The comparison between the present results and two previous sets of theoretical calculations [Pan, C. Starace, A. F. (1991). Physical Review A, 44(1), 324., and Moccia, R., Rahman, N. K., Rizzo, A. (1983). Journal of Physics B: Atomic and Molecular Physics, 16(15), 2737.] indicates that electron-electron correlation contributes appreciably to the 2-photon ionization dynamics.
Bulletin of the American Physical Society, 2016
x-ray photoelectron spectroscopy techniques for real-time studies of
Nature Communications
The double photoionization of a molecule by one photon ejects two electrons and typically creates... more The double photoionization of a molecule by one photon ejects two electrons and typically creates an unstable dication. Observing the subsequent fragmentation products in coincidence can reveal a surprisingly detailed picture of the dynamics. Determining the time evolution and quantum mechanical states involved leads to deeper understanding of molecular dynamics. Here in a combined experimental and theoretical study, we unambiguously separate the sequential breakup via D+ + OD+ intermediates, from other processes leading to the same D+ + D+ + O final products of double ionization of water by a single photon. Moreover, we experimentally identify, separate, and follow step by step, two pathways involving the b 1Σ+ and a 1Δ electronic states of the intermediate OD+ ion. Our classical trajectory calculations on the relevant potential energy surfaces reproduce well the measured data and, combined with the experiment, enable the determination of the internal energy and angular momentum di...
Physical Review Letters, 2007
Using H 2 and D 2 , we observe two-surface population dynamics by measuring the kinetic energy of... more Using H 2 and D 2 , we observe two-surface population dynamics by measuring the kinetic energy of the correlated ions that are created when H 2 (D 2) ionize in short (40-140 fs) and intense (10 14 W=cm 2) infrared laser pulses. Experimentally, we find a modulation of the kinetic energy spectrum of the correlated fragments. The spectral progression arises from a hitherto unexpected spatial modulation on the excited state population, revealed by Coulomb explosion. By solving the two-level time-dependent Schrödinger equation, we show that an interference between the net-two-photon and the one-photon transition creates localized electrons which subsequently ionize.
We present state-selective measurements on the NH_2^+ + H^+ and NH^+ + H^+ + H dissociation chann... more We present state-selective measurements on the NH_2^+ + H^+ and NH^+ + H^+ + H dissociation channels following single-photon double ionization at 61.5 eV of neutral NH_3, where the two photoelectrons and two cations are measured in coincidence using 3-D momentum imaging. Three dication electronic states are identified to contribute to the NH_2^+ + H^+ dissociation channel, where the excitation in one of the three states undergoes intersystem crossing prior to dissociation, producing a cold NH_2^+ fragment. In contrast, the other two states directly dissociate, producing a ro-vibrationally excited NH_2^+ fragment with roughly 1 eV of internal energy. The NH^+ + H^+ + H channel is fed by direct dissociation from three intermediate dication states, one of which is shared with the NH_2^+ + H^+ channel. We find evidence of autoionization contributing to each of the double ionization channels. The distributions of the relative emission angle between the two photoelectrons, as well as the ...
We investigate ultrafast dynamics of the lowest singlet excited electronic state in liquid nitrob... more We investigate ultrafast dynamics of the lowest singlet excited electronic state in liquid nitrobenzene using Ultrafast Transient Polarization Spectroscopy (UTPS), extending the well-known technique of Optical-Kerr Effect (OKE) spectroscopy to excited electronic states. The third-order non-linear response of the excited molecular ensemble is highly sensitive to details of excited state character and geometries and is measured using two femtosecond pulses following a third femtosecond pulse that populates the S1 excited state. By measuring this response as a function of time delays between the three pulses involved, we extract the dephasing time of the wave-packet on the excited state. The dephasing time measured as a function of time-delay after pump excitation shows oscillations indicating oscillatory wave-packet dynamics on the excited state. From the experimental measurements and supporting theoretical calculations, we deduce that the wave-packet completely leaves the S1 state su...
We present state-selective measurements on the NH_2^+ + H^+ and NH^+ + H^+ + H dissociation chann... more We present state-selective measurements on the NH_2^+ + H^+ and NH^+ + H^+ + H dissociation channels following single-photon double ionization at 61.5 eV of neutral NH_3, where the two photoelectrons and two cations are measured in coincidence using 3-D momentum imaging. Three dication electronic states are identified to contribute to the NH_2^+ + H^+ dissociation channel, where the excitation in one of the three states undergoes intersystem crossing prior to dissociation, producing a cold NH_2^+ fragment. In contrast, the other two states directly dissociate, producing a ro-vibrationally excited NH_2^+ fragment with roughly 1 eV of internal energy. The NH^+ + H^+ + H channel is fed by direct dissociation from three intermediate dication states, one of which is shared with the NH_2^+ + H^+ channel. We find evidence of autoionization contributing to each of the double ionization channels. The distributions of the relative emission angle between the two photoelectrons, as well as the ...
Review of Scientific Instruments
We report a novel experimental technique to investigate ultrafast dynamics in photoexcited molecu... more We report a novel experimental technique to investigate ultrafast dynamics in photoexcited molecules by probing the 3 rd-order nonlinear optical susceptibility. A non-colinear 3-pulse scheme is developed to probe the ultrafast dynamics of excited electronic states using the optical Kerr effect. Optical homodyne and optical heterodyne detection are demonstrated to measure the 3 rdorder nonlinear optical response for the S 1 excited state of liquid nitrobenzene, which is populated by 2-photon absorption of a 780 nm 40 fs excitation pulse.
Physical Chemistry Chemical Physics
3D momentum imaging investigation of the dynamics of dissociative electron attachment to formic a... more 3D momentum imaging investigation of the dynamics of dissociative electron attachment to formic acid, producing a hydride anion and either formyloxyl or hydrocarboxyl radicals.
Nature communications, Jan 22, 2017
The toolbox for imaging molecules is well-equipped today. Some techniques visualize the geometric... more The toolbox for imaging molecules is well-equipped today. Some techniques visualize the geometrical structure, others the electron density or electron orbitals. Molecules are many-body systems for which the correlation between the constituents is decisive and the spatial and the momentum distribution of one electron depends on those of the other electrons and the nuclei. Such correlations have escaped direct observation by imaging techniques so far. Here, we implement an imaging scheme which visualizes correlations between electrons by coincident detection of the reaction fragments after high energy photofragmentation. With this technique, we examine the H2 two-electron wave function in which electron-electron correlation beyond the mean-field level is prominent. We visualize the dependence of the wave function on the internuclear distance. High energy photoelectrons are shown to be a powerful tool for molecular imaging. Our study paves the way for future time resolved correlation i...
Molecular Physics, 2012
This article may be used for research, teaching, and private study purposes. Any substantial or s... more This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
Physical chemistry chemical physics : PCCP, Jan 15, 2018
We present a combined experimental and theoretical investigation of the electron dynamics and bod... more We present a combined experimental and theoretical investigation of the electron dynamics and body-frame angular dependence of valence photo-single ionization of CF4 and subsequent dissociation into CF3+ and F. Ionization from a valence t2 orbital shows overlapping shape resonances close to threshold that couple to the same total symmetry, leading to striking changes in the photoelectron angular distributions when viewed in the body-frame.
Abstract—We have developed a delay-line readout technique for microchannel plate detectors with a... more Abstract—We have developed a delay-line readout technique for microchannel plate detectors with an increased acceptance for multiple hit events compared to standard two-layer delay-line an-odes. This technique allows unambiguous determination of arrival time and position of at least two simultaneously detected particles, and/or to detect an even larger number of particles in a shower, as long as any two particles do not arrive both at the same time and at the same position within certain limits. We demonstrate and dis-cuss the abilities and limitations of this technique and the relevance for certain experimental tasks. Index Terms—Delay line, fragment imaging, imaging, micro-channel plate, multihit, three-dimensional (3-D) detection. I.
Chemical Science
We investigate interatomic Coulombic decay in NeKr dimers after neon inner-valence photoionizatio... more We investigate interatomic Coulombic decay in NeKr dimers after neon inner-valence photoionization [Ne+(2s-1)] using a synchrotron light source. We measure with energy resolution the two singly charged ions of the...